This is the perfect concoction for the Empathic Environment to whip up a good old Lightning Reveal. There's something sinister lurking in the shadows that the character(s) and perhaps audience is unaware of until lightning strikes. In that flash of lightning something is revealed hence, well, the Lightning Reveal.

Bonus points if the flash is so quick, the audience/characters are unsure if they saw anything at all.

Comic Books

Done beautifully in book three of Bone when Fone Bone, Thorn and Gran'ma Ben are on the run from the rat creatures in the middle of a storm. Lighting flashes light up the otherwise pitch black backgrounds, giving brief glimpses of the rat creature horde closing in, as well as when the Red Dragon appears and chases them away.

Film

In the 2nd adaption of Lord of the Flies, a lightning strike gives the viewer a better glimpse of Simon's bloody corpse in the water after Jack's tribe stabs him to death

In the opening scene of Van Helsing, Dracula's demonic visage is briefly visible when lightning strikes.

Happens during the climax of The Lion King when Simba reveals himself to Scar before the final confrontation.

Literature

In The Dresden Files: Storm Front, Morgan's appearance at the bar is revealed by lightning.

In Terry Pratchett's Discworld novel Reaper Man, Death knows that his replacement is not going to arrive until midnight because he stood on a hill while lightning flashed. He reasons that someone who does that would not arrive at 11:55 if he could make a dramatic entrance at the stroke of midnight.

In Lee Lightner's Warhammer 40000Space Wolf novel Wolf' Honour, when Ragnor and his company meet up with strange, wolf-like creatures, lightning flashes let them see the faces. (Much to Ragnor's horror. These creatures had haunted his dreams.)

Found in JRR Tolkien's Silmarillion. After being captured by Orcs, the hero Túrin accidentally kills his friend Beleg whom he mistakes for an Orc coming to torture him (in reality, he was trying to free him). Túrin realizes his mistake immediately when a flash of lightning illuminates the scene.

In David Weber'sSafehold series, at one point the Royal Guard is desperately fighting assassins in the rain. One moment, there is one Guardsman standing. The next, there is a flash of lightning, a roll of thunder (from the wrong direction) and there are two... One of them is a 26th Century cyborg. Guess what happens next.

Done in Queste, where Tertius Fume's ghost reveals itself to the crowd in the Wizard Tower in a flash of lightning.

In the H. P. Lovecraft short story The Lurking Fear, the first chapter ends with the narrator realizing that something other than one of his human companions was snuggled up to him on a cot in a reputedly haunted house when it gets up suddenly and a flash of lightning casts its shadow on the wall he's facing.

Live Action TV

Used brilliantly during the opening of an episode of CSI, showcasing the killer lurking in his victim's bedroom.

Parodied in an episode of Friends where Phoebe, suffering from chickenpox, is revealed to her long distance relationship boyfriend by a flash of lightning, causing him to jump. When she asks if she really looks that bad, he replies that he was just surprised by the lightning.

Happens in an episode of Only Fools and Horses where the trio are staying in Boycie's cottage. Of course, the escaped serial killer only gets shown when Del turns around, so the whole thing also ends up being a case of a Cassandra Truth.

Theater

According to William Goldman's book The Season, there was a Broadway play in 1967 called "A Day in the Death of Joe Egg." The show centers around the toll that taking care of a severely disabled daughter - a girl with cerebral palsy so bad she cannot even communicate - is taking on her parents. In one scene, the mother gives a despairing monologue, and at the end, there's a flash of lightning to show, just for an instant, her daughter skipping rope like any normal child. (You can imagine it being both scary and heartbreaking.)

Video Games

Occurs in the bonus case of Phoenix Wright: Ace Attorney. Phoenix's current case revolves around a case two years prior that may have been subject to evidence tampering. The primary witness of the previous case recalls two men fighting during a blackout, but remembers one instant, during a lightning strike, where she saw one man about to stab the other.

Subverted in Freefall. A secondary character answers a knock on his door on a dark and stormy night (While watching a werewolf movie!) and sees a bipedal wolf with large fangs. She's got severe hypothermia and is going into shock from the gash on her leg.

Family Guy plays with this in the episode where the kids find the money clip.

The opening theme to Batman: The Animated Series. Batman fights crooks in darkness, and the police wonder who it could be. The theme ends with the crooks tied up and a silhouette of Batman, standing on the roof of a building. A flash of lightning confirms his presence, before he disappears. Take a look at the opening, it's pretty awesome.

In the first part of "Two-Face," Harvey Dent is sitting in the psychiatrist's office, discussing his mental problems, with his Face Framed in Shadow. Suddenly, lightning strikes, and the dark half of his face lights up... as Two Face.

Tornadoes at nighttime can sometimes fall under this trope. A flash of lightning can sometimes illuminate an otherwise invisible funnel cloud or debris circulation, and storm spotters are trained to look on the horizon and under cloud bases for something that is not lightning but might be confused for it and that is far more indicative of tornado danger - power flashes from the tornado itself snapping power lines and blowing transformers.